# Understand a command line to create a matrix

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Mark Sc on 8 Oct 2021
Commented: Geoff Hayes on 8 Oct 2021
Hi all,
I am trying to write the following matlab line into another program, I already found it in the internet, it works perfectly, but I can not understand excatly how it work ??
clc; nelments= 3; npoint= 5;
connect=(1:npoint) + (npoint-1)*(0:nelments-1).'

Geoff Hayes on 8 Oct 2021
@Mark Sc - this is an interesting piece of code. Given that
>> x = (1:npoint)
x =
1 2 3 4 5
and that
>> y = (npoint-1)*(0:nelments-1).'
y =
0
4
8
we are trying to add a 1x5 matrix with a 3x1 matrix with the output being a 3x5. Looking at the plus for 2-D inputs, if one input is a column vector, and the other is a row vector then your output (in this case) will be that 3x5 matrix where we add 0 to each element of x to get the first row of the new matrix, 4 to each element of x to get the second row of the new matrix, and 8 to each element of x to get the third row.
>> x + y
ans =
1 2 3 4 5
5 6 7 8 9
9 10 11 12 13
Mark Sc on 8 Oct 2021
Thank you for clear explanation,
Not sure if possible to ask could we do the same in python ??
If so, could you provide it ??
Geoff Hayes on 8 Oct 2021
@Mark Sc - I tried doing something similar in Python but observed an error
Traceback (most recent call last):
File "py-add.py", line 4, in <module>
c=a+b
ValueError: operands could not be broadcast together with shapes (5) (3)
so from this one example it seems that it behaves a little differently than MATLAB. It shouldn't be too hard to write the code to do what you want though.